The U.S. Renewable Fuel Standards (RFS) mandate will require higher volumes of advanced biofuels to be produced in the near future. One method being developed to meet this mandate is the fast pyrolysis of biomass. Conventional biomass fast pyrolysis requires rapid heating of biomass in the absence of oxygen. Products include a solid carbonaceous char that contains the vast quantities of metals (e.g. Na, K, Mg) present in the biomass feedstock. The products also include a highly oxygenated pyrolysis oil (or pyoil) that is not practical for upgrading to a transportation fuel because of thermal stability issues associated with highly reactive oxygenated components. The remainder of the pyrolysis product is classified as non-condensable gas. To generate a viable transportation fuel, catalysts may be employed during the pyrolysis process. Catalysts such as zeolites can deoxygenate the primary products from pyrolysis to create an intermediate liquid that can be upgraded to a fuel using conventional refining methodology. Hydrogen may also be added to perform hydro-catalytic pyrolysis, which improves the quality of the product by significantly lowering the oxygen content, the acid content, etc. The use of hydrogen increases the yield of pyrolysis oil by hydrogenating the primary gaseous products, which removes oxygen as water instead of carbon oxides. The relatively low oxygen content intermediate produced is easily upgradeable to bio-derived fuels.
Unfortunately, when employing this process, the catalysts tend to rapidly deactivate when contacted by char fines composed of carbon and metals. Additionally, the char fines are often carried out of the pyrolyzer by entrainment with the pyrolysis vapor, resulting in a liquid product containing solids and metals that can negatively impact downstream processes.
There is a need to improve fast pyrolysis technology to allow for rapid catalytic upgrading of primary gaseous products into products that are fungible with current petroleum-derived liquid hydrocarbon fuels, while preventing char and associated metals from entrainment with these vapors to cause catalyst deactivation and equipment fouling, as well as increasing the instability of the product pyrolysis oil.